This invention relates to a bladed rotor for a gas turbine engine and is particularly concerned with the fixing of the aerofoil blades on such a bladed rotor.
Gas turbine engines commonly include an axial flow compressor that comprises a plurality of axially spaced apart bladed rotors. Each of the rotors comprises a disc carrying an annular array of radially extending aerofoil blades on its periphery. Each aerofoil blade is provided with a root at its radially inner end that locates in an appropriately shaped axially extending slot in the disc periphery. This root may conveniently be of the so-called "dovetail" configuration. The root is slid axially into its disc retention slot so that the dovetail configuration of the root and its retention slot provide radial retention of the blade.
It is necessary to provide some means for axially retaining each aerofoil blade in its disc slot. One way of achieving this is to position an axially extending removable clip between the base of each blade root and its corresponding retention slot. One end of the clip is bent around the disc and the other around the blade root so that the clip prevents axial movement of the blade in one direction. Movement in the opposite direction is prevented by a small integral location feature provided on the blade root that abuts the disc.
While such clips are effective in providing axial blade root retention, they do allow air to leak through the small gaps that inevitably exist between each blade root and its retention slot. Such leakage is undesirable in view of the detrimental effect that it can have upon overall compressor efficiency.
Another way of achieving axial aerofoil blade retention is to position an annular array of retention plates over the ends of the blade roots and the adjacent axial surface of the disc. Such plates are effective in preventing axial blade movement and also in preventing air leakage between the blade roots and their location slots. There are, however, difficulties in retaining the plates in position. One convenient way of providing plate retention is to locate each plate between radially spaced apart annular slots provided on the disc and on the platforms of the aerofoil blades. The radially inner slot is defined by the disc and is radially outwardly directed wherein the radially outer slot is defined by both the disc and the blade platform and is radially inwardly directed. It is necessary, however, to provide some way of preventing relative movement between the plates and the disc to avoid the blade/disc assembly becoming unbalanced. Clamps or other similar retention devices could be used to provide plate retention. However, such devices usually give rise to windage effects which in turn adversely affect compressor efficiency.
It is an object of the present invention to provide a gas turbine engine bladed rotor in which the aerofoil blades are fixed to the disc in such a manner that such difficulties are substantially avoided.